Murine ORAI2 splice variants form functional Ca2+ release-activated Ca2+ (CRAC) channels
Stefan Alfred Gross1, Ulrich Wissenbach, Stephan Ernst Philipp
1Institut für Experimentelle und Klinische Pharmakologie und Toxikologie, Universität des Saarlandes, 66421 Homburg/Saar, Germany.
The Journal of Biological Chemistry
|April 28, 2007
Summary
Murine ORAI2 variants, ORAI2L and ORAI2S, influence calcium release-activated calcium (CRAC) channel activity differently based on cell type. ORAI2S shows sensitivity to internal calcium and can inhibit CRAC channel formation.
Area of Science:
- Molecular Biology
- Cell Physiology
- Genetics
Background:
- Stimulation of membrane receptors activates phospholipase C, leading to calcium release-activated calcium (CRAC) channel activation.
- ORAI1 is a key pore subunit of CRAC channels, with STIM1 being essential for their activation.
Purpose of the Study:
- To investigate the genomic organization, tissue expression, and functional properties of murine ORAI2.
- To clone murine ORAI1, ORAI3, and STIM1 for comparative analysis.
Main Methods:
- Genomic analysis to identify loci for murine orai2.
- Northern blotting to determine tissue expression patterns of ORAI variants and STIM1.
- Co-expression studies in HEK 293 and RBL 2H3 cells to assess CRAC channel function.
Main Results:
- Two loci for murine orai2 were found, one intronless and one producing ORAI2 long (ORAI2L) and ORAI2 short (ORAI2S) splice variants.
- ORAI2 variants were highly expressed in brain, lung, spleen, and intestine; ORAI1, ORAI3, and STIM1 showed near-ubiquitous expression.
- ORAI2L and ORAI2S enhanced CRAC currents in HEK 293 cells but not RBL 2H3 cells, unlike ORAI1 which enhanced currents in both.
- ORAI2S-formed CRAC channels were sensitive to internal calcium inactivation and exhibited negative dominance when co-expressed with ORAI1 and STIM1.
Conclusions:
- The functional capacity of ORAI2 variants in forming CRAC channels is cell-type dependent.
- ORAI2S plays a significant role in modulating CRAC channel activity, including calcium sensitivity and potential inhibition.
- These findings highlight the complex regulation of CRAC channels by different ORAI isoforms and cellular context.
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